Recovery of a monoglyceride by azeotropic distillation with an alcohol

ABSTRACT

THE RECOVERY OF SURFACE-ACTIVE AGENTS FROM AQUEOUS SOLVENTS BY USE OF SUBSTITUTED, LOW CARBON ALIPHATIC ALOCHOL TO FORM A HETEROGENEOUS, MINIMUM BOILING POINT AZEOTROPE AND REMOVING SAID AZEOTROPE FROM SAID SURFACE ACTIVE AGENT BY CONVENTIONAL DISTILLATION AND EVAPORATION TECHNIQUES. THE PROCESS OF THIS INVENTION PERMITS THE RECOVERY OF SURFACE-ACTIVE AGENTS FROM HETEROGENOUS MIXTURES AND A REDUCTION OF FOAMING TO BELOW A LEVEL WHICH CONSIDERED SIGNIFICANT.

. 3,826,720 RECOVERY OF A MONOGLYCERIDE BY AZEO- TROPIC DISTILLATION WITH AN ALCOHOL Erlend Rupert Lowrey, Greenhills, Ohio, assignor to The Procter & Gamble Company, Cincinnati, Ohio No Drawing. Filed May 1, 1972, Ser. No. 249,051 Int. Cl. B01d 3/36; Cllb 3/12 US. Cl. 203-20 8 Claims ABSTRACT OF THE DISCLOSURE The recovery of surface-active agents from aqueous solvents by use of unsubstituted, low carbon aliphatic alcohol toform a heterogeneous, minimum boiling point azeotrope and removing said azeotrope from said surface active agent by conventional distillation and evaporation techniques. The process of this invention permits the recovery of surface-active agents from heterogeneous mixtures and a reduction of foaming to below a level which is considered significant.

BACKGROUND OF THE INVENTION This invention relates to the use of low carbon unsubstituted aliphatic alcohols in the formation of minimum boiling azeotropes for use in the separation of surface active agents from conventional aqueous extraction solvents.

During the preparation of some commercial products mixtures containing surface active agents are often formed as by-products. These surface active agents, when separated from heterogeneous mixtures, after often valuable in their own right as detergents, wetting agents, and emulsifiers. As a specific example of this glycerides may be produced by the esterification of free fatty acids or the 'alcoholysis of fatty acid esters with glycerol. The glycerides so produced, however, are in the form of a mixture which contains in addition to the monoglycerides a relatively large content of diand triglycerides. It has been found desirable to separate the monoglycerides from the diand triglycerides as the monoglyceride fraction possesses outstanding emulsifier properties while the diand triglycerides may be used more advantageously for other manufacturing purposes such as preparation of specific melting point fats, e.g. synthetic cocoa butter.

The conventional method of separation is by use of a liquid-liquid extraction process using wet methanol and an alkane, usually hexane. The diand triglycerides migrate to the alkane while at the same time the monoglycerides migrate to the methanol, thus resulting in two solutions which may be separated. However, problems have arisen regarding the separation of the wet methanol from the monoglycerides to provide isolated monoglycerides suitable for emulsifier purposes. It has been previously found that the use of normal distillation or evaporation techniques results in excessive foaming, especially during the removal of the final 20% of the water-methanol mixture, and thus results in an undesirable decrease in the percentage of monoglyceride recovered. Specifically, as much as 50% of the monoglycerides may be lost due to foaming. This problem has been effectively eliminated by the process of this invention.

The principal advantage derived from the use of unsubstituted aliphatic alcohols of low carbon content in the separation process is a decrease, below a level of significance, of the rate of foaming observed on the final isolation of the surface active fraction. The Working mechanism of this invention is the ability of unsubstituted, low carbon, aliphatic alcohols, especially butanol, to combine with extraction solvents such as methanol and water to form a heterogeneous, minimum boiling azeotrope which may be conveniently distilled or evaporated with- Patented July 30, 1974 out causing excessive foaming normally characteristic of such separation processes.

An azeotrope is a mixture of two or more liquid compounds whose boiling point does not change as vapor is generated and removed. Stated differently, a heterogeneous, minimum boiling azeotrope results when two or more liquid phases of partially miscible liquids boil, producing a vapor whose composition is the same as the average composition of two or more liquid phases. Azeotropic distillations are fractionations that are facilitated by deliberately adding a new component which shifts the vaporliquid equilibrium in a favorable direction.

The process of this invention is intended for use in the separation of surface-active agents in general from aqueous solvents. The three basic categories of said surface-active agents are: detergents, wetting agents, and emulsifiers. Each separate category is surfac-active because of the same basic chemical mechanism, the primary distinction among them being the nature of the surfaces involved. Detergents are defined as substances which reduce the surface tension of water; and more specifically surfaceactive agents which concentrate at oil-water interfaces. Common examples of detergents are sodium salts of fatty acids. Wetting agents are surfactants which reduce water surface tension and thus allow the water to penetrate more easily into another material. Examples of wetting agents are soaps and certain alcohols. An emulsifier is defined as a surface-active agent which, then used even in small percentages, causes the formation of a stable suspension of two or more immiscible liquids. Monoglycerides are common examples of emulsifiers.

The advantages resulting from use of the process of this invention are specific to the separation of surfaceactive agents due to the unique foaming characteristics exhibited by surface-active agents. The actual mechanism of foaming is not clearly understood; however, it is theorized that in order to form the foam in the first place it is probable that the concentration of the aqueous solvent in aqueous solvent-surfactant mixtures becomes greater at the air-liquid'interface. Thus, the surface tension of the liquid solvent is lowered, enabling bubbles of foam to form. In the specific reference to surface-active agents it is theorized that during the distillation or evaporation of aqueous solvents the presence of a surface-active agent stabilizes the bubbles of foam that are normally formed during such operations and hence allows rapid proliferation of foam and the resulting decrease in surface-active agent recovery during separation steps. For a more complete discussion of foaming, the foaming mechanism, and foam prevention, see Bailey's Industrial Oil and Fat Products, Third Edition, 1964, pages 395-396.

Particularly preferred surface-active agents which may be more efliciently isolated and recovered by practice of this invention are glycerides and especially monoglycerides. Glycerides in general constitute valuable commercial materials and may be used effectively as emulsifiers, lubricants, and in cosmetics, in addition to other related uses. Glycerides are widely used for technical purposes and have been used extensively by the food industry. The production of glycerides normally involves the formation of a heterogeneous chemical mixture which contains a glyceride fraction, the most common example being those glycerides based on fatty acids which occur naturally in fats and oils. This production can be followed by a liquidliquid extraction whereby aqueous solvents are used to separate the various glyceride components, i.e. monoglycerides, diglycerides and triglycerides. However, a problem frequently encountered in the industrial production of glycerides is the removal of the glyceride fractions from aqueous solvents. Especially troublesome is the foaming which occurs on attempts to distill or evaporate the solvents. It is possible with the practice of this invention to eliminate foami g t fitsi lk B L tSt e r m stfir ciency and convenience of the glyceride production process by as much as 50%.

I The use of alcohols in general as azeotropic. agents an patents and literature. However, thefuse of loivbarbpn,

unsubstituted, aliphatic alcohols, e. g. butanol, is not disclosed by theprior art and, intact, the teachin gspfi'the prior art are away from the use of low carbon, alcohols as azeotropic separation agents. For purposes ofthisap plication the term low carbon alcohol" refers to those monohydric, aliphatic alcohols having a carbon content of from 2 to 7 carbon atoms. The definition includes primary; secondary and tertiary alcohols. Examples of low carbon alcohols are ethanol, propanol, butanol, pentanol, isobutanol, and the like. It must be remembered, however, that the proper alcohol will depend on the. specific surface-active agent being separated.

More specifically, prior attempts to control foaming and to form azeotropic mixtures for the removal of surface-active agents have involved primarily the use of alcoholic compounds having 8 or more carbon atoms and usually involving alcohols having from 14 to 25 carbon atoms. In addition, specific anti-foaming agents have been developed, i.e. polyhydric alcohols (alcohol containing 3 or more hydroxy groups). However, these anti-foaming agents have had little success and each has had significant deficiencies in practical application.

Azeotropic separations are generally known. In this regard see Azeotropic Separations, Coates, Chemical Engineering, May 16, 1960, pages 121-136; Azeotropic Separation, Othmer, Chemical Engineering Progress, vol. 9, No. 6, June 1962, pages 67-78; and The Phase Relations of Binary Systems That Form Azeotropes, Skaates and Kay, Chemical Engineering Science, Vol. 19, 1964, pages 431-444. However, the use of the particular azeotropic agents and the significant results obtained from this invention are not known to be described in the prior art.

While the prior art contains several references to the use of alcohols as azeotropic extraction agents none discloses the use of unsubstituted low carbon aliphatic alcohols, e.g. butanol, in the isolation and/or extraction of monoglycerides. The prior art patents fall generally into three areas of distinction. The first of such areas includes those patents disclosing the use of alcohols having molecular structures of 8 carbon atoms or more as azeotropic extraction agents. Sample patents teaching the use of alcohols having 8 carbon atoms or more are US. Pat. 2,797,- 198 issued-to Chappell in 1954. This patent requires the alcohol to be solid and to contain 14 to 25 carbon atoms.

Other'representative patents teaching the use of 'high caring and claiming the application of the separation characteristics of alcohols to aid in the removal of specific identified non-surface-active products such as casein; see for example, US. Pat. 2,220,700 (1938) issued to Atwood and disclosing n-butyl alcohol for antifoaming purposes.

A third class of distinct but related patents is that which discloses and claims only-the use of polyols-or substituted of oils and oil compositions have been proposed. For instance, mechanical devices have been proposed for de stroying or breaking foam as it .is formed.Likewise, the incorporation of certain oil-soluble-compounds in the oil h as been proposed as ameans f L Y UH-.3

for preventing foaming; such compounds being called anti foa'ni'a'gents. These and other methods have, however, met with very limited success. A complaint generally applicable to all of the above-described unsatisfactory methods is that extraneous andrundesirable compounds are inevitably intrgcluced intp the isolated final productv I Therefore, an object of at-his invention is, the fcnfnatigpn of an azeotropic mixture containing an. unsubstituted low carbon aliphatic alcohol, water and methanoland the-"use of this azeotropic mixture'to separate surface active agents from aqueous solvents without'also separating extraneous undesired products.

Further, it is an object of thisjnvention to provide an azeotropic mixture for use in the above-mentioned separation which prevents excessive' foaming during the re moval and surface-active agentisolation'processes. The method of accomplishing these and other objects will become apparent from the detailed description of the invention set out below.

SUMMARY OF THE INVENTION The present invention is based 'on'the discovery that by forming a heterogeneous, minimum boiling azeotrope with an unsubstituted, low carbon, aliphatic alcohol an aqueous extraction solvent may be more easily removed from a surface-active agent without the excessive foamingnormally associated with such a' removal. The preferred alcohol for use in connection with this inventionis butanol; however, other unsubstituted aliphatic alcoholshaving a carbon content of C to C, are also usable.

DETAILED DESCRIPTION OF THE INVENTION ess is measurably increased, i.e. as mu'ch as50'%', by the practiceof this invention.

The practice of thprocess of this invention'involves the fir'ststep of adding to the surface-active agent-aqueous extraction solvent mixture at'least a stoichiometrically determined quantity of unsubstituted, 'aliphatic low carbon alcohol. Amounts in excess of stoichiometrically' 'determined amounts can be used without aifecting' the process of this invention The additioi'r'of the low" carbon a1- cohol causes the formation of a heterogeneous minimum boiling azeotrope. It should be noted 'here'that some alcohols will be viableazeotropic agents for some aqueous extraction solvents while others will not. The azeotro'pe once formed can then be conveniently removed by any of a number of commercial techniques. The most common of such techniques are evaporation and/or distillation. The exact method of evaporation or-di'stillation will vary depending on the particular a'zeotropeand the particular surface-active agent sought to be isolated:

A preferred embodiment of this invention involves the separation and isolation of monoglycerides from mixtures containing mono-, di-, and triglycerides. The mono-, di-, and triglyceride mixture is initially subjected to a'liquidliquid extraction proces. The extraction solvents normally used are wet methanol and hexane, althoughother alkane's, alcohols, and hydrocarbon solvents may be substituted for the hexane. i

The exact amount of each extraction solvent will vary depending on the composition of g'lyceride mixture. In an especially preferred embodiment of this invention the alkane flows countercurrently to the wet methanol solution. This countercurrent flow renders the alkane convenient to standard removal procedures. Both the diglycerides and triglycerides migrate to the alkane which is countercurrently flowing with respect to the wet methanol and, therefore, easily removable. At the same time the monoglycerides migrate to the wet methanol which is then isolated for further processing.

The resulting isolated mixture therefore Contains methanol, water and monoglycerides. It is, of course, desirable to separate the surface-active agent from the aqueous solvent with the maximum efliciency possible. One of the primary factors decreasing the efiicient recovery of the isolated surface-active agent is the above-mentioned foaming at the liquid-air interface during the final evaporation or distillation steps. This foaming has been found to be the direct result of the presence of the various surfaceactive agents sought to be isolated. Therefore, according to the practice of this invention foaming can be prevented by adding at least a stoichiometrically determined amount of unsubstituted low carbon alcohol, preferably butanol, to the methanol-water-monoglyceride mixture. The amount of low carbon alcohol, e.g. butanol, required in accordance with this invention will vary with the amount of water present, the tendency of the oil itself to foam, the particular alcohol employed, and the severity of the conditions to which the oil is subjected. This addition initiates the formation of a heterogeneous, minimum boiling azeotrope. Conventional evaporation and distillation techniques can be employed to evaporate the water-methanolbutanol azeotrope and thereby isolate the monoglyceride.

It is important to note that according to this invention evaporation and/ or distillation can be accomplished without significant monoglyceride loss from foaming. The process of this invention represents an extremely significant improvement in the efliciency of the process of monoglyceride separation, isolation, and recovery.

A-particular preferred process deviates from the above disclosed process by forming the heterogeneous minimum boiling azeotrope with only the final of the methanol-water-monoglyceride mixture. This is preferred because it has been found through experimentation that it is primarily the final 20% of the monoglyceride-methanolwater solution that foams significantly. Therefore, butanol is added to the final 20% in at least stoichiometric amounts and processed exactly according to the process previously described. This results in the same amount of monoglyceride being isolated and recovered while at the same time significantly saving on expenses since only the final 20% requires the addition of low carbon alcohols to effect eflicient separation.

Example 1 A heterogeneous mixture was obtained comprising the end product of a reaction to completion of triglyceride with glycerine in the presence of a sodium methoxide catalyst. The reaction was allowed to proceed until an equilibrium state had been reached. The resulting product contained monoglycerides, 50% diglycerides, and 25% triglycerides. This mixture was then continuously pumped into the central portion of a countercurrent separation column at a rate of 2 pounds per hour. At the same time flowing into the top of the separation column was a mixture of methanol and water consisting of 90% methanol and 10% water. The water-methanol mixture was fiowing into the separation column at the rate of pounds per hour. Simultaneously hexane was introduced into the bottom of said column at a rate of 20 pounds per hour. The monoglycerides migrated to the wet methanol solution and the diglycerides and triglycerides migrated to the hexane solution. Since the two solutions were countercurrently flowing, the separation of the two solutions was extremely clear. Specifically, greater than 98% of the monoglycerides in the initial heterogeneous mixtures migrated to the wet methanol. The wet methanol-monoglyceride mixture left the bottom of the separation column having approximately a 6% concentration of monoglycerides.

The hexane-diglyceride-triglyceride mixture was then stored for furture processing. The methanol-water-monoglyceride mixture was then prepared for further treatment in accord with the process of this invention. Specifically, the monoglyceridemethanol-water mixture was placed in a still. Heat was applied beginning at room temperature and increasing gradually to 150 F. At this point a significant amount of methanol had been distilled off. Additional heat was applied to begin the removal of water. However, if the temperature had been taken all the way up to the boiling point of water (212 F.), a significant amount of foaming would have been noticed. It was therefore necessary to stop the application of heat at a point between 150 F. and 212 F. at which foaming began. At this point it was calculated that approximately of the methanolwater mixture had been evaporated. Then, enough butanol was added to the remaining mixture to form an azeotropic mixture with all of the water. The amount of butanol added was in excess of the stoichiometric amount. Specically, the volume of the methanol-water-monoglyceride mixture was measured and an equal volume of butanol was added thus ensuring an excess of the stoichiometric amount. Once again heat was applied beginning at room temperature and building up gradually to temperatures of approximately 250 F. At this temperature all of the methanol, water, and butanol had been distilled and the resulting product was pure isolated monoglyceride. This separation process was accomplished without any significant losses resulting from foaming.

Example 2 The surface-active agent is separated from a heterogeneous mixture by the process of Example 1 with the single exception being that propanol is used in the place of butanol. The process conditions and the amounts of propanol are identical to the process conditions and amounts of butanol used in Example 1. The separation results are found to be identical to the results obtained in Example 1. Specifically, foaming is decreased below a level of significance while correspondingly the efficiency of the surface active agent recovery process is increased.

Example 3 A surface-active agent is separated from a heterogeneous mixture by the process of Example 1 with the single exception being that isopropyl alcohol is used in the place of butanol. The process conditions and the amount of isopropyl alcohol are identical to the process conditions and amount of butanol used in Example 1. The separation results are found to be identical to the results obtained in Example 1. Specifically foaming is decreased below a level of significance while correspondingly the efficiency of the surface-active agent recovery process is increased.

Example 4 A surface-active agent is separated from a heterogeneous mixture by the process of Example 1 with the single exception being that secondary butanol is used in the place of butanol. The process conditions and the amount of secondary butanol are identical to the process conditions and amount of butanol used in Example 1. The separation results are found to be identical to the results obtained in Example 1. Specifically, foaming is decreased below a level of significance while correspondingly the efficiency of the surface-active agent recovery process is increased.

Example 5 A surface-active agent is separated from a heterogeneous mixture by the process of Example 1 with the single exception being that an evaporation process step is used in place of the distillation step of Example 1. The separation results are found to be identical to the results obtained in Example 1. Specifically foaming is decreased below a level of significance while correspondingly the efliciency of the surface-active agent recovery process is increased.

Example 6 A surface-active agent is separated from a heterogeneous mixture by the process of Example 1 with the single exception being that pentane is used in the place of hexane in the separation of the glyceride components. The process conditions and the amount of pentane are identical to the process conditions and amount of hexane used in Example 1. The glyceride separation results are found to be identical to the results obtained in Example 1. Specifically, the diand triglycerides are found to migrate to the pentane which can be conviently removed by the countercurrent separation technique employed in Example 1. At the same time an extremely clear separation is obtained with an insignificant percent of the diand triglycerides not migrating to the pentane.

I claim:

1. A process for the isolation of a monoglyceride from a water-solvent mixture containing a glyceride mixture, which comprises:

(a) adding to said glyceride water-solvent mixture a monohydric unsubstituted aliphatic alcohol having from 2 to 7 carbon atoms in an amount sufiicient to form an azeotropic mixture with said water-solvent mixture; and

(b) vaporizing the azeotropic mixture thereby providing said monoglyceride in isolated form.

2. The process of claim 1 wherein said solvent is represented by methanol.

3. The process of claim 1 wherein said monohydric unsubstituted aliphatic alcohol is represented by butanol.

4. A process for the isolation of a monoglyceride from a mixture of glycerides comprising:

(a) subjecting the mixture of glycerides to a liquidliquid extraction using water, methanol and an alkane;

(b) separating the water-methanol-monglyceride containing extract from the alkane extract;

(c) adding to the water-methanel-monoglyceride extract a monohydric unsubstituted aliphatic alcohol having from 2 to 7 carbon atoms in an amount sufficient to form an azeotropic mixture with said watermethanol mixture; and

(d) vaporizing said azeotropic mixture thereby providing said monoglyceride in isolated form.

5. The process of claim 4 wherein said monohydric aliphatic alcohol is represented by butanol.

6. The process of claim 5 wherein said alkane is represented by hexane.

7. The process of claim 5 wherein the alkane extraction solvent is flowing countercurrently to the water-methanol mixture.

8. A process for the isolation of a monoglyceride from a mixture of mono-, ditriglyceride consisting ofi (a) subjecting the mixture of mono-, di-, and triglyceride to a liquidliquid extraction using water, methanol and hexane; I

(b) separating the resulting hexane extract containing said mixture of diand triglyceride from the watermethanol extract containing said monoglyceride;

(c) vaporizing the resulting water-methzinol-monoglyceride extract to the point where foaming begins;

((1) adding butanol in an amount sufiicient to form an azeotrope with the remaining water-methanol-monoglyceride mixture of (c); and

(e) vaporizing the resulting azeotropic mixture from said monoglyceride thereby providing the monoglyceride in isolation form.

References Cited UNITED STATES PATENTS 2,614,971 10/1952 Burton 203-18 2,663,682 12/1953 Traeger et al 203- 2,591,671 4/1952 Catterall 203-18 2,674,609 4/1954 Beal et al 203-63 2,905,677 9/1959 Fevig et al. 260-4285 3,006,938 10/1961 West et al 260428.5 3,025,314 3/1962 King et a] 260-4285 WILBUR L. BASCOMB, 1a., Primary Examiner US. Cl. X.R. 

